Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $108.87   7.102%   $116.6019   $116.60   $116.60   $116.60  
  Purchase #2 $163.97   10.287%   $180.8376   $180.84   $180.85   $180.80  
  Purchase #3 $63.74   12.461%   $71.6826   $71.68   $71.70   $71.70  
  Purchase #4 $188.91   11.232%   $210.1284   $210.13   $210.15   $210.10  
  Purchase #5 $10.37   9.696%   $11.3755   $11.38   $11.40   $11.40  
  Purchase #6 $247.67   13.478%   $281.051   $281.05   $281.05   $281.10  
  Purchase #7 $210.87   12.649%   $237.5429   $237.54   $237.55   $237.50  
  7 purchase totals = $994.40       $1,109.2199   $1,109.22   $1,109.30   $1,109.20